Topic: Hits 15 PSI then drops to 7? (Read 17230 times)

patsmx5 · « **on:** August 29, 2009, 07:37:08 PM »

Ok it's never done this before. Usually just goes to whatever the boost is set for and holds SOLID. Now it's hitting peak boost and the tapers down the longer I'm in boost. Like dropping from 15 PSI to 6-7..

And I could feel it of course I was like WTF it would step out in second then fall flat and hook up again.

It wasn't doing this yesterday. Today I removed the old hacked

rigged VR sensor bracket I used to use and made a new one. The old one would vibrate at certain engine speeds and the engine would go "off" and then snap back on. It got to the point I couldn't go over 4500, so I fixed it today. Now it will works fine. But this all of a sudden? Only thing I can think is that the timing may be 4-5* more retarded than it was before. But wouldn't that make it overshoot? This is baffling, and 15 pounds was fucking RIPPING till it falls down.

Screenshot from a datalog, 1st, 2nd, 3rd.

patsmx5 · « **Reply #1 on:** August 29, 2009, 08:41:37 PM »

Running a 38mm knockoff tial WG, GT3271 turbo FWIW.

patsmx5 · « **Reply #2 on:** August 29, 2009, 10:26:40 PM »

Checked all the lines to the WG and BOV, they look fine. Drove it again and still same thing. Brake boosted it and more of the same.

stealthiskey · « **Reply #3 on:** August 29, 2009, 10:27:14 PM »

could be small boost leak

patsmx5 · « **Reply #4 on:** August 29, 2009, 10:30:49 PM »

Yeah. I checked all the connections and they all looked fine. Guess I should pressure test them to be sure though. It's all T-bolted though and never leaked before.

stealthiskey · « **Reply #5 on:** August 29, 2009, 10:43:04 PM »

Looking at your datalog, the first graphs, in second and third gear. Notice the boost falls off as RPMs increase above a certain point. That point appears to be roughly the same for both 2 and 3 gear.

Theory: boost leaks. Turbo is maxed out pushing all the air it can. at lower rpm the engine draws less air so even though some boost is leaking it still hits full psi and wg opens. but when engine draws more air at higher rpm, turbo cant spin faster to push more air, so boost drops off. Your exhaust backpressure would also be higher than norm, cuz the WG never opens at high rpm, thereby making car feel even slower.

could also be exhaust leak or WG problem.

My tbolt silicone couplers held for a while, then they started leaking for no reason. boost would go up to 10 at ~ 3k rpm, but drop down to 5 by 6500

patsmx5 · « **Reply #6 on:** August 29, 2009, 10:45:31 PM »

yeah, I see what you're saying. And yes there is DEFINATELY a RPM/boost drop correlation. I brake boosted it for like 5-6 seconds at a steady RPM and boost statyed the same. When I let of the brake it took off and boost dropped.... Guess I'll be doing a boost leak check tomorrow.

patsmx5 · « **Reply #7 on:** August 29, 2009, 10:47:02 PM »

Also 99% sure it's not an exhaust leak, as the car is very quiet and it's had pre-turbo leaks before and they are obvious as they're very loud. Also visually inspected the WG and manifold and they look good with no signs of leaking.

Ravage70 · « **Reply #8 on:** August 30, 2009, 01:52:07 AM »

Thats not your boost thats the Dow last October

patsmx5 · « **Reply #9 on:** August 30, 2009, 01:40:51 PM »

Quote from: Ravage70 on August 30, 2009, 01:52:07 AM

Thats not your boost thats the Dow last October

Haha, no kidding....

I tightened up all the T-bolts. They weren't as tight as I thought they were. Also went over every vacuum hose on the engine to make sure they weren't cut or damaged, and ziptied the few that weren't. Also took the BOV off and made sure it wasn't sticking or stuck open. It looks moves fine. If it ever quits raining and the roads dry up I'll go run it and see if it's any better. I visually inspected every inch of the charge pipes and couplers and they look good. If it's still messing up I'll do a boost leak check. Maybe something on the IC is leaking.

glustic · « **Reply #10 on:** August 30, 2009, 03:06:41 PM »

Your IC could be leaking? Sounds like youve gone over every vac line, IC pipe and coupler. Maybe one of the welds on the IC has a crack?

patsmx5 · « **Reply #11 on:** August 30, 2009, 03:36:07 PM »

Well, just drove it and it's still not holding boost. Yeah, perhaps my egay IC is leaking, dunno. Guess I'll pressure check it. Off to Lowes for some PVC caps.

glustic · « **Reply #12 on:** August 30, 2009, 04:02:51 PM »

Quote from: patsmx5 on August 30, 2009, 03:36:07 PM

Well, just drove it and it's still not holding boost. Yeah, perhaps my egay IC is leaking, dunno. Guess I'll pressure check it. Off to Lowes for some PVC caps.

Get a free valve stem from your local tireshop... Thats what I did

patsmx5 · « **Reply #13 on:** August 30, 2009, 05:12:00 PM »

Did a leak test. Pressurized the pipes from the outlet of the turbo to the inlet of the intake manifold. The air intake temp sensor was leaking a little around the threads of it. At 20 PSI in the system you could put your hand by it and feel the air, but it was a small leak. Fixed that with JB-weld. Now when I do it the BOV leaks a tiny tiny bit, just enough to hear. But that's without putting pressure on it to keep it closed, so.... After 22 PSI the BOV opens and dumps air. But up to 20 no leaks other than a tiny little bit from the BOV.

FWIW, that intake temp sensor has probably leaked forever as I just drilled a hole in a piece of tubing and screwed the bastard into it, no sealants, no cutting threads, etc. but it's fixed now, but I highly doubt that was causing me to loose any boost.

Robb · « **Reply #14 on:** August 30, 2009, 05:30:21 PM »

Sir, dont forget about your injector seals. They have bit me in the ass before.

patsmx5 · « **Reply #15 on:** August 30, 2009, 06:08:32 PM »

I hooked the pipe back to the intake manifold and shot it to 20 PSI, no leaks there either.

patsmx5 · « **Reply #16 on:** August 30, 2009, 06:10:39 PM »

Talked to JD and he says it could be the wastegate, specifically the diaphram. So I'm gonna order a tial replacement one and put it in next weekend hopefully.

patsmx5 · « **Reply #17 on:** August 30, 2009, 06:54:00 PM »

So on egay a tial replacement diaphragm is 62 shipped. Is there anyone else that has a better price? I only paid 65 or 75 for the damn WG shipped...

patsmx5 · « **Reply #18 on:** August 31, 2009, 10:24:17 AM »

Could it be my stock muffler? I have 3" exhaust to the back then it goes into a 2" pipe and into the stock muffler. The wastegate also ties back into the exhaust. Maybe the backpressure is just too high.

reddevil · « **Reply #19 on:** September 01, 2009, 02:22:50 AM »

Sometmes this vacumn port is bocked. Make sue its filled.

caged · « **Reply #20 on:** September 01, 2009, 06:50:52 AM »

Quote from: patsmx5 on August 31, 2009, 10:24:17 AM

Could it be my stock muffler? I have 3" exhaust to the back then it goes into a 2" pipe and into the stock muffler. The wastegate also ties back into the exhaust. Maybe the backpressure is just too high.

Your exhaust is a pos. I didnt think you would of still had it rigged up like that. drop the rear 2inch pipe+muffler and have a drive.

patsmx5 · « **Reply #21 on:** September 01, 2009, 09:27:26 AM »

Well the stock exhaust rigged like that was supposed to be temporary. Just to see how quiet it would be. But then I never redid it... Complex, good to hear that someone else has seen this be the problem before.

Teg2boo · « **Reply #22 on:** September 01, 2009, 09:52:32 AM »

Isnt you that have 5 mufflers on your car? Cherry bomb catback

patsmx5 · « **Reply #23 on:** September 01, 2009, 09:54:25 AM »

yeah three 3" cherry bombs then drops to 2" and into a stock muffler.

jagojon3 · « **Reply #24 on:** September 01, 2009, 10:49:02 PM »

I contacted tial about a replacement diaphragm, sent them my wg and they replaced it for free and gave the whole unit a good cleaning.

bigdaddyvtec · « **Reply #25 on:** September 02, 2009, 01:02:44 AM »

if the diaphram is fucked up its going to creep to all hell, not get lower.....

patsmx5 · « **Reply #26 on:** September 02, 2009, 09:06:22 AM »

Quote from: bigdaddyvtec on September 02, 2009, 01:02:44 AM

if the diaphram is fucked up its going to creep to all hell, not get lower.....

My thinking exactly. I can't see how it would go lower. And pulling the wastegate on my car would take a few hours, so I'd rather not if it's isn't the problem.

Kenny Rogers · « **Reply #27 on:** September 02, 2009, 11:42:37 AM »

I'm thinking it's the exhaust. At lower RPM's the 2" exhaust is sufficient. After that it's clearly hitting a threshold as to how much exhaust can be removed from your engine. At this threshold it's putting stress on the system with backpressure (losing HP), and keeping the turbo from spinning freely and maintaining 15 psi.

Kenny Rogers · « **Reply #28 on:** September 02, 2009, 12:32:12 PM »

Easy test: Take off the section of 2" exhaust... either past the cherry bomb, or if that's welded run open DP just to test this theory. I'm almost certain this is the problem.

patsmx5 · « **Reply #29 on:** September 02, 2009, 12:43:20 PM »

Yeah I think it's the muffler. This weekend I'm probably gonna pull the muffler and see what happens. It will still have about 2' of 2" pipe, but that's a lot less restrictive than the muffler itself.

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Author Topic: Hits 15 PSI then drops to 7? (Read 17230 times)